1. Technical Field
This invention relates to elevators in general, and to elevator safety brake apparatus in particular.
2. Background Information
Safety regulations concerning the operation of elevators require a safety brake on the elevator car and sometimes on the counterweight of the elevator to stop the elevator in the event of a gross overspeed condition. Typically, the overspeed condition is detected by a governor rope assembly comprising a governor sheave, a governor rope, a centrifugally actuated governor rope brake, and a tension sheave. The governor rope is formed in a closed loop extending between the governor sheave at the top of the hoistway and the tension sheave at the bottom of the hoistway. A linkage, consisting of a rod or a cable pigtail, for example, connects the governor rope to a safety apparatus aboard the vehicle for actuating the safety brakes.
In normal operation, the linkage pulls the governor rope along at the same speed as the vehicle. In the event of a downward overspeed condition, the centrifugally actuated governor rope brake applies a brake force to the governor rope, and thereby causes the governor rope to travel at a slower speed than the vehicle. As a result, the linkage extending between the rope and the safety apparatus actuates the apparatus and therefore the safety brakes as well. The safety brakes progressively stop the vehicle by applying a frictional force to the guiderails guiding the vehicle.
One of the more popular safety brakes, also known as a progressive safety, is that disclosed by Koppensteiner in U.S. Pat. No. 4,538,706, which is hereby incorporated by reference thereto. Koppensteiner discloses a safety brake which straddles an elevator rail and is attached to the frame of the vehicle. The safety brake employs a brake surface on one side of the rail and a leaf spring and roller assembly on the opposite side. When the elevator governor activates the safety, an actuating rod causes the roller to wedge between the leaf-spring assembly and a rail face. As a result, the brake lining located on the opposite side of the rail contacts the opposite rail face, producing a braking force on the elevator car.
Safety brakes are generally attached directly to the frame of the car or the counterweight by conventional fasteners. The large load applied to the safety brake in an emergency stop is transferred to the frame of the vehicle by one or more tongues extending out from the back of the brake and into slots within the vehicle frame. While advantageous for transferring the load, these tongues make it impossible to remove the safety while the vehicle is positioned between the guiderails. Specifically, the distance between the guiderails less the assembled width of the vehicle and safety brakes is not great enough to allow the tongue(s) to be withdrawn completely from the frame. As a result, one of the guiderails must be removed before the safety and/or the vehicle can be removed. A person of skill in the art will recognize that removing a guiderail is an arduous job and therefore a distinct disadvantage.
Safety apparatus aboard an elevator car or counterweight for actuating the safety brakes is known in the art. U.S. Pat. No. 4,083,432 to Lusti discloses a safety apparatus for use with a centrifugally operated governor. The apparatus includes a compensating means to prevent the inertial force of a flexible governor member from operating the safety brakes. U.S. Pat. No. 5,230,406 to Poon discloses a safety brake arrangement for preventing overspeeding in the upward and downward direction.
A person of skill in the art will recognize that it is an advantage to minimize the complexity of an elevator safety arrangement and also to increase the reliability of the safety arrangement. A person of skill in the art will further recognize that is an advantage to decrease the amount of time necessary to actuate the safeties, since the speed of the vehicle accelerates by virtue of gravity.